Investment Securities - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended							12 Months Ended
	Jun. 30, 2012	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Mortgage-backed Securities ("MBS") [Member] Security Y	Jun. 30, 2013 U.S. Government and government sponsored enterprises ("GSE") [Member]	Dec. 31, 2012 U.S. Government and government sponsored enterprises ("GSE") [Member]	Jun. 30, 2013 U.S. Government and government sponsored enterprises ("GSE") [Member] Mortgage-backed Securities ("MBS") [Member]	Jun. 30, 2013 SASCO RM-1 2002 [Member]	Dec. 31, 2011 SASCO 2002-RM1 Class O Securities [Member]	Jun. 30, 2013 SASCO 2002-RM1 Class O Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities				142
Securities amortized cost		$ 833,672,000	$ 886,031,000				$ 730,300,000
Weighted average duration of MBS portfolio				5.4
Securities pledged as collateral		436,500,000
Proceeds from sale of investment securities	504,200,000	220,300,000
Gain from sale of investment securities	15,400,000	2,500,000
Unamortized premiums		25,000,000
Unaccreted discounts		115,000
Owned investment securities		690,238,000	111,339,000		2,004,000	2,008,000
Total unrealized losses on securities		24,736,000	717,000		3,000	2,000
Purchase price of municipal bonds		51,100,000
Trading securities, par value								12,600,000	2,500,000
Investments purchase percentage									100.00%
Trading securities, fair value										$ 6,400,000